The present invention relates to a thermal transfer printer having a thermal head for transferring ink from an ink tape to a sheet of print paper, and more particularly to a thermal transfer printer capable of printing operation while the thermal head is reciprocally moving in opposite directions.
Various information processing apparatus such as word processors of today employ thermal transfer printers. FIG. 1 of the accompanying drawings schematically shows a conventional thermal transfer printer. The thermal transfer printer includes a platen 1 against which a sheet of print paper 2 is held. The paper sheet 2 can successively be fed along in response to rotation of the platen 1. The thermal transfer printer also has a carriage 3 reciprocally movable axially along the platen 2. The carriage 3 supports thereon a thermal head 4 and an ink tape 5 which is coiled around takeup reel 6a and a supply reel 6b that are mounted on the carriage 3.
For printing operation, the carriage 3 is first positioned at a lefthand end of its range of reciprocating movement when printing is to be started. After the paper sheet 2 has been placed in the printer, the carriage 3 is moved in the direction of the arrow. At this time, the thermal head 4 is biased toward the platen 1 so as to press the ink tape 5 against the paper sheet 2. The ink tape 5 is wound by the takeup reel 6a as it is fed along in a direction opposite to the direction of movement of the carriage 3. During this time, thermal dots on the thermal head 4 are selectively heated to melt a desired pattern of ink on the ink tape 5 and transfer the ink pattern from the ink tape 5 to the paper sheet 2. By selectively heating the thermal dots on the thermal head 4 in timed relation to the movement of the thermal head 4, desired characters, symbols, and/or graphic patterns of matrices of dots can be transferred to the paper sheet 2.
While the thermal transfer printer can print sharper characters or other patterns than other printers such as wire-dot printers, it has a slow printing speed. The thermal transfer printer is particularly disadvantageous in that it is incapable of printing operation while the thermal head is reciprocally moving in opposite directions unlike the wire-dot printer. Such a problem arises out of the following condition: In the thermal transfer printer, the ink tape 5 is pressed against the paper sheet 2 by the thermal head 4. During rightward movement of the carriage 3, the speed of relative movement between the platen 1 (the paper sheet 2) and the ink tape 5 must be nil at all times. If the paper sheet 2 and the ink tape 5 are moved relative to each other, they would slide against each other, with the result that the paper sheet 2 would get smeared with ink and characters to be transferred with heat from the thermal head 4 would become unclear. In addition, the ink tape 5 would be cut off under undue tension, and be liable to get wrinkled and jammed between the paper sheet 2 and the thermal head 4. For the reasons described above, the speed V of movement of the carriage 3 in one direction and the speed v of movement of the ink tape 5 in the opposite direction are equalized so that the speed of relative movement of the ink tape 5 and the paper sheet 2 will be nil.
After one line has been printed on the paper sheet 2 in the rightward direction, therefore, it is impossible to print characters in a return stroke of leftward movement of the carriage 3 while at the same time feeding the ink tape 5 in said opposite direction. It would be possible however to eliminate the speed of relative movement between the paper sheet 2 and the ink tape 5 during the return stroke of the carriage 3 by feeding the ink tape 5 in a direction opposite to that of leftward movement of the carriage 3. This would result in the reuse of the once-consumed length of the tape 5, which would print unclear characters or the like due to ink shortage.